ARLINGTON, Va. (WSAZ) -- The U.S. Department of Labor's Mine Safety and Health Administration says that four mining operations have received letters putting them on notice about a potential pattern of violations of mandatory health or safety standards.

The four mines that received warning letters are Argus Energy WV LLC's Deep Mine No. 8 in Wayne County, W.Va.; Pike Floyd Mining Inc.'s No. 3 Mine in Pike County, Ky.; Ten-Mile Coal Co. Inc.'s No. 4 Mine in Harrison County, W.Va.; and Noranda Alumina LLC's Gramercy Facility in St. James County, La.

In addition, two non-producing mines have received warning letters.. They are D & C Mining Corp.'s D & C Mining Corp. in Harlan County, Ky., and Hecla Mining Co.'s Lucky Friday Mine in Shoshone County, Idaho.

MSHA implemented improved screening criteria in 2010 to better identify mines that have been subject to closure orders, including for serious issues such as failing to correct violations cited by MSHA, unwarrantable failures to comply with health or safety standards, failure to provide miners with required training and imminent dangers in the mine. The criteria better identify mines where these tools have been used but have not been sufficient to improve compliance. The criteria also consider whether a mine has a high number of significant and substantial, or S&S, violations involving elevated negligence as well as a mine's injury severity rate, targeting operations that have an above-average injury severity measure.